Although a variety of current theories have described several genetic mechanisms by which aging is controlled, they all view life-span as a character in the species' adaptive strategy. Theories of demography and life history share this view in predicting the type of selective forces that establish patterns of longevity and senescence. Experiments described here test the prediction that continuous reproduction early or late in life selects respectively for reduced or increased life-span with associated effects in other life history features. A few previous experiments have examined the effects of early and late reproduction in the context of the Lansing Effect, however, they have either failed to control important factors affecting longevity or else yielded highly unusual results. Where the first experiment proposed shows the effect of age-specific reproduction on longevity and other features, a second experiment tests the converse. That is, selection for longevity will be applied directly to populations, to show the effects of increased or decreased life-span on reproduction and other life history features. Selection in both experiments will be applied to a 4-way hybrid population of Drosophila strains. Characters including longevity, fertility, fecundity and various aspects of development will be measured as adaptation proceeds.